
A gamma distribution is adopted for the penalty parameter \(\gamma _k\)  to enforce the column-wise sparsity [1]}:
\(\!\!\!\!\!p(\lbrace \gamma _k\rbrace _{k=1}^{K}|\imath _{\gamma })\!=\!\prod _{k=1}^{K}\!\!\mathrm {gamma}(\gamma _k|\delta ,\delta )\!\!=\!\!\prod _{k=1}^{K}\!\!\gamma _k^{\delta -1}\exp (-\delta \gamma _k),\) 
